AMEREN CORP
S-3D, 1998-01-05
METAL MINING
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<PAGE>   1






        AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON JANUARY 5, 1998 
                                      Registration Statement No. 33-___________

           Post-Effective Amendment No. 1 to Registration Statement No. 33-64165
================================================================================

                                 UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                    FORM S-3

            REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933

                           -----------------------

                               AMEREN CORPORATION
             (Exact name of registrant as specified in its charter)

             STATE OF MISSOURI                                    43-1723446
       (State or other jurisdiction                             (IRS Employer
    of incorporation  or organization)                       Identification No.)

                              1901 Chouteau Avenue
                           St. Louis, Missouri  63103
                                 (314) 621-3222
    (Address, including zip code, and telephone number, including area code,
                  of registrant's principal executive offices)

                           -----------------------

                DONALD E. BRANDT, Senior Vice President, Finance
                          JAMES C. THOMPSON, Secretary
                1901 Chouteau Avenue, St. Louis, Missouri  63103
                                 (314) 621-3222
(Names, address, including zip code, and telephone number, including area code,
of agents for service)

                        CALCULATION OF REGISTRATION FEE

<TABLE>
<CAPTION>
===========================================================================================================================
   TITLE OF EACH CLASS       AMOUNT TO BE       PROPOSED MAXIMUM     PROPOSED MAXIMUM          AMOUNT OF
   OF SECURITIES TO BE        REGISTERED         OFFERING PRICE     AGGREGATE OFFERING     REGISTRATION FEE
        REGISTERED                                PER UNIT (1)             PRICE                  (2)
- ---------------------------------------------------------------------------------------------------------------------------
   <S>                     <C>                  <C>                 <C>                    <C>

      COMMON STOCK,
     $.01 PAR VALUE        4,200,000 SHARES         $42.2816           $177,582,720             $53,813
===========================================================================================================================
</TABLE>

  (1)    Calculated in accordance with Rule 457(c) on the basis of the average
         of the high and low sales prices of Union Electric Company Common
         Stock as reported on the New York Stock Exchange Composite Tape on
         December 26, 1997.

  (2)    800,000 shares of Common Stock to be offered and sold under the Plan
         were previously registered (Form S-4 Registration Statement, Reg.  No.
         33-64165) and are carried forward hereby.  The amount of filing fee
         associated with the Common Stock that was previously paid with such
         earlier registration statement is $10,949.


         APPROXIMATE DATE OF COMMENCEMENT OF PROPOSED SALE TO THE PUBLIC: From
time to time after this Registration Statement becomes effective.

         If the only securities being registered on this Form are being offered
pursuant to dividend or interest reinvestment plans, please check the following
box:[x]

         If any of the securities being registered on this Form are to be
offered on a delayed or continuous basis pursuant to Rule 415 under the
Securities Act of 1933, other than securities offered only in connection with
dividend or interest reinvestment plans, please check the following box:[ ]

         If this Form is filed to register additional securities for an
offering pursuant to Rule 462(b) under the Securities Act, please check the
following box and list the Securities Act registration statement number of the
earlier effective registration statement for the same offering.  [ ]___________

         If this Form is a post-effective amendment filed pursuant to Rule
462(c) under the Securities Act, check the following box and list the
Securities Act registration statement number of the earlier effective
registration statement for the same offering.  [ ]___________

         If delivery of the prospectus is expected to be made pursuant to Rule
434, please check the following box.  [ ]
================================================================================
<PAGE>   2

PROSPECTUS

                               AMEREN CORPORATION

                                     DRPLUS
                 DIVIDEND REINVESTMENT AND STOCK PURCHASE PLAN

    DRPlus (the "Plan") of Ameren Corporation (the "Company") is designed to
provide Participants with a convenient way to purchase shares of the Company's
common stock, $.01 par value ("Common Stock"), and to reinvest all or a portion
of the cash dividends paid on the Company's Common Stock and the Preferred
Stock of the Company's subsidiaries (the "Eligible Securities"), including
Union Electric Company ("Union Electric") and Central Illinois Public Service
Company ("CIPS"), in additional shares of Common Stock.

    Participants in the Plan may:

    -    Make an initial investment in Common Stock with a cash investment of
         at least $50.
    -    Reinvest all or a portion of cash dividends paid on Eligible
         Securities in additional shares of Common Stock.  
    -    Increase their investment in Common Stock by making optional cash 
         investments of at least $25 at any time.  
    -    Receive, upon request, certificates for whole shares of Common Stock 
         credited to their Plan accounts.  
    -    Deposit certificates representing Common Stock into their Plan 
         accounts for safekeeping.  
    -    Sell shares of Common Stock credited to their Plan accounts.

    Shares of Common Stock purchased under the Plan will, at the option of the
Company, be newly issued shares or treasury shares purchased directly from the
Company, or shares purchased in the open market or in privately negotiated
transactions.  Any open market or privately negotiated purchases will be
effected through an Independent Agent (as hereinafter defined) selected by the
Company.  The Common Stock is listed on the New York Stock Exchange under the
ticker symbol AEE.  The Company is initially registering 5,000,000 shares with
the Securities and Exchange Commission in connection with the Plan.

    The purchase price of newly issued or treasury shares of Common Stock
purchased under the Plan for an Investment Date (as hereinafter described) will
be the average of the high and low sales prices of the Common Stock on the
Investment Date reported as New York Stock Exchange Composite Transactions as
published in the Midwest Edition of The Wall Street Journal or other similar
financial publication.  The price of shares of Common Stock purchased in the
open market or in privately negotiated transactions will be the weighted
average price per share of the aggregate number of shares purchased with
respect to the relevant Investment Date.  The Company will pay the costs of
administration of the Plan; however, Participants will bear the costs of any
brokerage commissions and any applicable transfer taxes and service charges
related to shares purchased or sold under the Plan.

    For each meeting of shareholders, Participants will receive proxy cards
which will enable them to vote both shares registered in their names and shares
credited to their Plan accounts.

    To the extent required by applicable law in certain jurisdictions, shares
of Common Stock offered under the Plan to certain persons are offered only
through a registered broker/dealer in such jurisdictions.

    This Prospectus contains a summary of the material provisions of the Plan
and should be retained for future reference.

    EFFECTIVE DECEMBER 31, 1997 THE PLAN REPLACES, BY AMENDMENT AND
RESTATEMENT, THE DIVIDEND REINVESTMENT AND STOCK PURCHASE PLAN (THE "UNION
ELECTRIC PLAN") OFFERED BY UNION ELECTRIC AND THE AUTOMATIC DIVIDEND
REINVESTMENT AND STOCK PURCHASE PLAN (THE "CIPSCO PLAN") OFFERED BY CIPSCO
INCORPORATED ("CIPSCO").  ALL ACCOUNTS AND ALL ELECTIONS, NOTICES, INSTRUCTIONS
AND AUTHORIZATIONS UNDER THE UNION ELECTRIC PLAN AND THE CIPSCO PLAN WILL
AUTOMATICALLY CONTINUE UNDER THE PLAN, AND PARTICIPANTS IN THE UNION ELECTRIC
PLAN AND THE CIPSCO PLAN WILL CONTINUE AS PARTICIPANTS IN THE PLAN.  NO ACTION
BY CURRENT PARTICIPANTS IN THE UNION ELECTRIC PLAN AND THE CIPSCO PLAN IS
REQUIRED TO CONTINUE PARTICIPATION IN THE PLAN.  IF, AFTER REVIEWING THIS
PROSPECTUS, A PARTICIPANT IN THE UNION ELECTRIC PLAN OR THE CIPSCO PLAN DOES
NOT WISH TO CONTINUE PARTICIPATION IN THE PLAN, SUCH PARTICIPANT MUST DELIVER A
WRITTEN REQUEST TO THE INVESTOR SERVICES DEPARTMENT OF AMEREN SERVICES COMPANY,
AS DESCRIBED HEREIN.

- --------------------------------------------------------------------------------
THESE SECURITIES HAVE NOT BEEN APPROVED OR DISAPPROVED BY THE SECURITIES AND
EXCHANGE COMMISSION OR ANY STATE SECURITIES COMMISSION NOR HAS THE SECURITIES
AND EXCHANGE COMMISSION OR ANY STATE SECURITIES COMMISSION PASSED UPON THE
ACCURACY OR ADEQUACY OF THIS PROSPECTUS.  ANY REPRESENTATION TO THE CONTRARY IS
A CRIMINAL OFFENSE.
- --------------------------------------------------------------------------------


                The date of this Prospectus is January 5, 1998.



<PAGE>   3

                             AVAILABLE INFORMATION

     The Company is subject to the informational requirements of the Securities
Exchange Act of 1934, as amended (the "Exchange Act"), and in accordance
therewith files reports, proxy statements and other information with the
Securities and Exchange Commission (the "Commission").  Reports, proxy
statements and other information filed by the Company may be inspected and
copied at the public reference facilities maintained by the Commission at Room
1024, 450 Fifth Street, N.W., Washington, D.C. 20549, and at the Commission's
Regional Offices at 500 West Madison Street, Suite 1400, Chicago, Illinois
60661 and at 7 World Trade Center, Suite 1300, New York, New York 10048.
Copies of such material may be obtained from the public reference section of
the Commission, 450 Fifth Street, N.W., Washington, D.C. 20549, at prescribed
rates.  Such reports, proxy statements and other information concerning the
Company may also be inspected at the offices of the New York Stock Exchange, 20
Broad Street, New York, New York 10005 on which exchange the Common Stock of
the Company is listed.  The Commission maintains a Web site that contains
reports, proxy statements and other information regarding registrants, such as
the Company, that file electronically with the Commission.  The address of such
site is: (http://www.sec.gov).  In addition, such reports, proxy statements and
other information concerning the Company can be inspected at the principal
office of the Company, 1901 Chouteau Ave, St. Louis, Missouri 63103, telephone
(314)-621-3222.

     This Prospectus does not contain all of the information set forth in the
Registration Statement on Form S-3 (together with all amendments and exhibits
thereto, the "Registration Statement"), which the Company has filed with the
Commission under the Securities Act of 1933, as amended (the "Securities Act").
Statements contained or incorporated by reference herein concerning the
provisions of documents are necessarily summaries of such documents, and each
statement is qualified in its entirety by reference to the Registration
Statement.

                INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE

     The following documents, previously filed with the Commission by CIPSCO
(File No. 1-10628), Union Electric (File No. 1-2967) or the Company pursuant to
the Securities Exchange Act of 1934, as amended, are incorporated by reference
in this Registration Statement:

     1.   CIPSCO'S Annual Report on Form 10-K for the year ended December 31,
1996.

     2.   CIPSCO's Quarterly Reports on Form 10-Q for the quarters ended March
31, 1997, June 30, 1997 and September 30, 1997.

     3.   CIPSCO's Current Reports on Form 8-K dated March 20, November 24,
December 16 and December 31, 1997.

     4.   Union Electric's Annual Report on Form 10-K for the year ended
December 31, 1996.

     5.   Union Electric's Quarterly Reports on Form 10-Q for the quarters
ended March 31, 1997, June 30, 1997 and September 30, 1997.

     6.   Union Electric's Current Reports on Form 8-K dated December 16 and
December 31, 1997.

     7.   The Company's Current Report on Form 8-K dated December 31, 1997.

     8.   The Company's Registration Statement on Form S-4 (Reg. No. 33-64165),
filed November 13, 1995, which includes a description of the Common Stock of
the Company.

     All documents subsequently filed by the Company pursuant to Sections
13(a), 13(c), 14 or 15(d) of the Exchange Act after the date of this Prospectus
and prior to the termination of the offering of the Common Stock offered hereby
shall be deemed to be incorporated by reference in this Prospectus and to be a
part hereof from the date of filing of such documents.  Any statement contained
herein or in a document incorporated or deemed to be incorporated by reference
herein





                                       2



<PAGE>   4

shall be deemed to be modified or superseded for purposes of this Prospectus to
the extent that a statement contained herein or in any other subsequently filed
document which also is or is deemed to be incorporated by reference herein
modifies or supersedes such statement.  Any such statement so modified or
superseded shall not be deemed, except as so modified or superseded, to
constitute a part of this Prospectus.

     The Company will provide without charge to each person, including any
beneficial owner, to whom a copy of this Prospectus has been delivered, on the
written or oral request of such person, a copy of any and all of the documents
referred to above which have been or may be incorporated in this Prospectus by
reference, other than exhibits to such documents which are not specifically
incorporated by reference into the information that this Prospectus
incorporates.  Requests for such copies should be directed to the Investor
Services Department, Ameren Services Company, Post Office Box 66887, St. Louis,
Missouri 63166-6887, telephone number 1-800-255-2237.

                                  THE COMPANY

     The Company will be a registered public utility holding company under the
Public Utility Holding Company Act of 1935, as amended.  The principal utility
operating subsidiaries of the Company are Union Electric Company ("Union
Electric") and Central Illinois Public Service Company ("CIPS").  Union
Electric was incorporated in Missouri in 1922 and is successor to a number of
companies, the oldest of which was organized in 1881.  Union Electric, which is
the largest electric utility in the State of Missouri, supplies electric
service in territories in Missouri and Illinois having an estimated population
of 2,600,000 with an area of approximately 24,500 square miles, including the
greater St.  Louis area.  Retail gas service is supplied by Union Electric in
90 Missouri communities and in the City of Alton, Illinois and vicinity.  CIPS,
organized in 1902, serves 317,000 retail electricity customers and 166,000
natural gas customers in central and southern Illinois.  Union Electric and
CIPS became subsidiaries of the Company pursuant to mergers which became
effective on December 31, 1997.

                                USE OF PROCEEDS

     Because the extent of the requirements of Plan Participants cannot be
predicted and because such requirements may be satisfied by either the issuance
of new shares of Common Stock by the Company or the purchase of shares of
Common Stock by an Independent Agent in the open market, the number of shares
of Common Stock, if any, that the Company ultimately will sell under the Plan,
and the prices at which such shares will be sold, is not known.  If new shares
of Common Stock are issued by the Company under the Plan, the proceeds from the
sale will be used for repayment of short-term or long-term indebtedness, for
working capital or for other general corporate purposes.  If shares are
purchased by an Independent Agent for Participants in the open market, the
Company will not receive any proceeds from such sales.


                            DESCRIPTION OF THE PLAN
PURPOSE

1.   WHAT IS THE PURPOSE OF THE PLAN?

     The purpose of the Plan is to provide Participants (see Question 6) with a
convenient way to purchase shares of Common Stock, $.01 par value, ("Common
Stock") of Ameren Corporation (the "Company") and to reinvest all or a portion
of the cash dividends paid on the Company's Common Stock and on the Preferred
Stock of the Company's subsidiaries (together, the "Eligible Securities") in
additional shares of Common Stock.

     EFFECTIVE DECEMBER 31, 1997 THE PLAN REPLACES, BY AMENDMENT AND
RESTATEMENT, THE DIVIDEND REINVESTMENT AND STOCK PURCHASE PLAN (THE "UNION
ELECTRIC PLAN") OFFERED BY UNION ELECTRIC COMPANY AND THE AUTOMATIC DIVIDEND
REINVESTMENT AND STOCK PURCHASE PLAN (THE "CIPSCO PLAN") OFFERED BY CIPSCO
INCORPORATED.  ALL ACCOUNTS AND ALL ELECTIONS, NOTICES, INSTRUCTIONS AND
AUTHORIZATIONS UNDER THE UNION ELECTRIC PLAN AND THE CIPSCO PLAN WILL
AUTOMATICALLY CONTINUE UNDER THE PLAN, AND PARTICIPANTS IN THE UNION ELECTRIC
PLAN AND THE CIPSCO PLAN WILL CONTINUE AS







                                       3




<PAGE>   5

PARTICIPANTS IN THE PLAN.  NO ACTION BY CURRENT PARTICIPANTS IN THE UNION
ELECTRIC PLAN AND THE CIPSCO PLAN IS REQUIRED TO CONTINUE PARTICIPATION IN THE
PLAN.  IF, AFTER REVIEWING THIS PROSPECTUS, A PARTICIPANT IN THE UNION ELECTRIC
PLAN OR THE CIPSCO PLAN DOES NOT WISH TO CONTINUE PARTICIPATION IN THE PLAN,
SUCH PARTICIPANT MUST DELIVER A WRITTEN REQUEST TO THE INVESTOR SERVICES
DEPARTMENT OF AMEREN SERVICES COMPANY, AS DESCRIBED IN QUESTION 20.


FEATURES

2.   WHAT ARE THE MAIN FEATURES OF THE PLAN?

     #    Non-shareholders of legal age who are customers of the Company or its
          subsidiaries (a "Customer") may enroll in the Plan by making a
          minimum initial cash investment of $50 to purchase Common Stock under
          the terms of the Plan.

     #    Non-shareholders of legal age who are employees of the Company or its
          subsidiaries (an "Employee") may enroll in the Plan by authorizing a
          minimum payroll deduction investment of $25 per pay period to
          purchase Common Stock under the terms of the Plan.

     #    Participants may elect to have cash dividends on all or a portion of
          their shares of Common Stock or Preferred Stock automatically
          reinvested.  Dividend payments not reinvested will be paid to
          Participants by check or through electronic direct deposit.

     #    Participants may make Optional Cash Investments (including by
          authorizing direct debit from their personal bank accounts) in a
          minimum amount of $25 per transaction after the initial investment
          and up to a maximum of $120,000 per calendar year for the purchase of
          Common Stock.

     #    Full investment of funds is possible under the Plan because both full
          and fractional shares will be credited to Participants' Plan
          accounts.

     #    Participants may deposit their Common Stock certificates, at no cost,
          in their Plan accounts for safekeeping.

     #    Personal record keeping is simplified by the Company's issuance of
          statements showing account activity.  STATEMENTS OF ACCOUNT ARE A
          PARTICIPANT'S CONTINUING RECORD OF TRANSACTIONS AND SHOULD BE
          RETAINED FOR TAX PURPOSES.

     #    Participants may sell shares of Common Stock held or deposited in 
          their Plan accounts.

     #    By utilizing volume commission discounts from Independent Agents, the
          Plan is able to provide investors with an economical means to
          purchase and sell shares of the Company's Common Stock.


ADMINISTRATION

3.   WHO ADMINISTERS THE PLAN?

     Ameren Services Company ("Ameren Services"), a wholly-owned subsidiary of
the Company, will administer the Plan through its Investor Services Department
("Investor Services").  Among other things, Ameren Services will receive and
hold Participants' funds pending investment in additional shares of Common
Stock, effect transfers of Common Stock, keep a continuous record of
participation and prepare and send to each Participant statements of their Plan
account.  The responsibilities of Ameren Services in connection with the
administration of the Plan are administrative in nature and, in large part, are
consistent with the responsibilities of Ameren Services in acting as registered
transfer agent for the Company.





                                       4



<PAGE>   6

     If the Company elects to meet the requirements of Participants by
purchasing shares of Common Stock in the open market, an Independent Agent will
act on behalf of Participants in buying such shares.  The Independent Agent
will also sell Plan shares on behalf of Participants.

     THE COMPANY RESERVES THE RIGHT TO INTERPRET AND REGULATE THE PLAN AS
DEEMED NECESSARY OR DESIRABLE.  NEITHER THE COMPANY NOR ITS INDEPENDENT AGENTS
WILL BE LIABLE FOR ANY ACT DONE IN GOOD FAITH OR FOR ANY OMISSION TO ACT IN
GOOD FAITH, INCLUDING, WITHOUT LIMITATION, ANY CLAIM OF LIABILITY ARISING OUT
OF FAILURE TO TERMINATE A PARTICIPANT'S ACCOUNT UPON THE PARTICIPANT'S DEATH
PRIOR TO RECEIPT OF WRITTEN NOTICE OF SUCH DEATH, PROVIDED THAT THE COMPANY
SHALL NOT BE RELIEVED FROM ANY LIABILITY IMPOSED UNDER ANY FEDERAL, STATE OR
OTHER APPLICABLE SECURITIES LAW WHICH CANNOT BE WAIVED.  YOU SHOULD RECOGNIZE
THAT THE COMPANY CANNOT ASSURE YOU OF A PROFIT OR PROTECT YOU AGAINST A LOSS ON
SHARES PURCHASED OR SOLD UNDER THE PLAN.

4.  WHO SHOULD I CONTACT WITH QUESTIONS CONCERNING THE PLAN AND ITS
    ADMINISTRATION?

     You may contact the Company with questions concerning the Plan by writing
to:

                            Ameren Services Company
                            Investor Services Department
                            P.O. Box 66887
                            St. Louis, Missouri 63166-6887

or by calling Investor Services locally at 314-554-3502 or toll-free at
1-800-255-2237.

     Ameren Services acts as the transfer agent for all securities issued by
Ameren Corporation and its subsidiaries.

5.   MAY THE PLAN BE MODIFIED OR DISCONTINUED?

     The Company reserves the right to suspend, modify or discontinue the Plan
at any time including but not limited to the right to modify the fees and
commissions charged to Participants.  Any suspension, major modification or
discontinuance of the Plan will be announced by the Company to all
Participants.


PARTICIPATION

6.   WHO IS ELIGIBLE TO PARTICIPATE IN THE PLAN?

     All holders of Eligible Securities (that is, the Common Stock of the
Company and the Preferred Stock of the Company's subsidiaries), Customers of
the Company or its subsidiaries and Employees of the Company or its
subsidiaries are eligible to be Participants in the Plan.

     A Plan Prospectus and enrollment information will be furnished upon
request made to Investor Services.

7.   HOW DOES A HOLDER OF ELIGIBLE SECURITIES PARTICIPATE?

     Participants who hold Eligible Securities may join the Plan by completing
the Enrollment Form and returning it to Investor Services.  A Participant who
owns Eligible Securities that are registered in a name other than the
Participant's (for example, in the name of a broker or bank nominee) and who is
not a Customer or an Employee, may also participate in the Plan, subject to
certain limitations regarding the Eligible Securities held in such other name.
(Contact Investor Services for information concerning Participation by such
beneficial owners.)

     The Enrollment Form allows a Participant to choose a reinvestment option
for participation in the Plan.  By checking the appropriate box a Participant
may select:





                                       5



<PAGE>   7

     -    FULL DIVIDEND REINVESTMENT - Automatic reinvestment of cash dividends
          on all Eligible Securities registered in the name of the Participant
          and on all Plan shares credited to the Participant's account.

     -    PARTIAL DIVIDEND REINVESTMENT - Receipt of cash dividends on a
          portion of the Eligible Securities registered in the name of the
          Participant and/or a portion of the Plan Shares credited to the
          Participant's account, and automatic reinvestment of the cash
          dividends on the remainder of the Participant's shares.

     -    NO DIVIDEND REINVESTMENT - Receipt of cash dividends on all Eligible
          Securities registered in the name of the Participant and on all Plan
          shares credited to the Participant's account.

     Participants may change their reinvestment options by completing the
correspondence portion of their statement of account or an Enrollment Form and
sending it to Investor Services.  Changes will become effective as soon as
practicable after they are received.

8.   HOW DOES A CUSTOMER PARTICIPATE?

     A Customer may apply for enrollment in the Plan by completing and
returning a Plan Application Form, together with a check in an amount not less
than $50, nor more than $120,000, made payable to "Ameren Corporation".

     The Plan Application Form requires each applicant to certify residency.
It also allows the applicant to decide the amount of their initial investment
(not less than $50) which will be used to purchase shares of the Company's
Common Stock.  The Plan Application Form allows the applicant to choose a
reinvestment option for participation in the Plan. (See Question 7).

9.   HOW DOES AN EMPLOYEE PARTICIPATE?

     An Employee may join the Plan at any time by enrolling in the same manner
as any other eligible person described under Questions 7 or 8 or by completing
a Plan Payroll Deduction Authorization Form.


DIVIDEND REINVESTMENT

10.  HOW AND WHEN WILL CASH DIVIDENDS BE REINVESTED?

     If a Participant has elected full or partial dividend reinvestment on the
Eligible Securities registered in their name and/or their Plan shares, the
Company will reinvest those dividends in additional shares of the Company's
Common Stock.  The source of Common Stock to be purchased under the Plan may
be, at the discretion of the Company, authorized but unissued Common Stock or
shares of Common Stock purchased on the open market by an Independent Agent.

     If the Company is meeting the requirements of the Plan with Common Stock
purchased in the open market, an Independent Agent will determine the exact
timing of such purchases and the number of shares to be purchased, depending on
the amount of reinvested dividends, market conditions and the requirements of
federal securities laws, and the purchased shares will be credited to a
Participant's Plan account as of the applicable Investment Date.  If the
Company elects to issue authorized but unissued shares of its Common Stock,
these shares will be issued by the Company and credited to a Participant's Plan
account by the Company as of the applicable Investment Date.  The determination
of the price for purchases of Plan shares is explained in Question 17.

     If a Participant's Enrollment Form is received by Investor Services on or
before the record date with respect to any Common Stock or Preferred Stock cash
dividend payment date, then the





                                       6



<PAGE>   8

dividend payable on such payment date will be used to purchase additional
shares of Common Stock as of such payment date (an Investment Date).  If the
Enrollment Form is received after the record date with respect to any such cash
dividend payment date, the reinvestment of dividends will start with the
dividend payment next following such payment date.

     Each cash dividend payment date on the Eligible Securities will be an
Investment Date under the Plan; accordingly, cash dividends payable on each
Common Stock dividend payment date and on each Preferred Stock dividend payment
date, which are to be reinvested, will be invested in Common Stock as of such
dividend payment date.  Common Stock cash dividend payment dates will normally
be on or about the last business day of March, June, September and December;
and Preferred Stock cash dividend payment dates are currently the last day of
March, June, September and December (for CIPS Preferred Stock) and the 15th day
of February, May, August and November (for Union Electric Preferred Stock).


OPTIONAL CASH INVESTMENTS

11.    WHO IS ELIGIBLE TO MAKE OPTIONAL CASH INVESTMENTS?

       All Plan Participants, whether or not they have authorized the
reinvestment of dividends, are eligible to make Optional Cash Investments.

12.    HOW ARE OPTIONAL CASH INVESTMENTS MADE?

       A Plan Participant may make an initial cash investment when enrolling by
enclosing a check with the Enrollment Form.  Checks should be made payable to
"Ameren Corporation," and returned in the envelope provided with the Enrollment
Form.  Thereafter, Optional Cash Investments may be made by using the cash
investment form attached to the statement of account, by Automatic Cash
Investment (see Question 13) or by Employee payroll deduction (see Question 9).
Please contact Investor Services for additional cash investment forms.

13.    WHAT IS THE AUTOMATIC CASH INVESTMENT OPTION OF THE PLAN AND HOW DOES IT
       WORK?

       The Automatic Cash Investment option offers Participants in the Plan a
direct debit service.  Optional Cash Investments are electronically withdrawn
from your personal checking or savings account on a regular monthly basis and
used to purchase Common Stock.  The direct debit from  your personal bank
account will be shown on the monthly statement from your financial institution.
In addition, you will receive a statement from Investor Services detailing the
cash received and shares purchased.

       The Automatic Cash Investment option may be authorized for regular
monthly amounts from $25 to $10,000.  Funds authorized for investment through
the Automatic Cash Investment option will be debited approximately three days
prior to each Optional Cash Investment Date.  (See Question 15)

       For an Automatic Cash Investment application, contact Investor Services.

14.    WHAT ARE THE LIMITATIONS ON MAKING OPTIONAL CASH INVESTMENTS?

       Optional Cash Investments cannot be less than $25 per investment.  The
maximum invested in Plan Shares by any Participant cannot exceed $120,000 for
any calendar year.

15.    WHEN WILL OPTIONAL CASH INVESTMENTS BE INVESTED?

       The option to make cash investments is available to you at any time.
The dates on which Optional Cash Investments are used to purchase Common Stock
are determined solely at the discretion of the Company, although purchases on
behalf of Plan Participants will be made at least once a month.  Purchases may
be made over a period of several days in the case of market





                                       7



<PAGE>   9

purchases.  All such purchases will be aggregated and credited to Participants'
accounts on the Optional Cash Investment Date occurring on or after receipt of
the Optional Cash Investment.  There will be an Optional Cash Investment Date
on or about the last day of each month.  Participants will receive a notice at
the beginning of each year specifying the Optional Cash Investment Dates for
such year.

       Cash received after an Optional Cash Investment Date will be held by the
Company until, and will be invested as of, the next Optional Cash Investment
Date.  No interest will be paid by the Company on any cash investments received
and held by the Company pending investment.


PURCHASES

16.    HOW MANY SHARES OF COMMON STOCK WILL BE PURCHASED?

       No one can predict the number of shares that will be purchased for you
during a particular purchase period, and you cannot direct the Company to
purchase a specific number of shares.  The number of shares purchased for you
under the Plan depends on the amount of funds you have available for investment
and the price of the shares.  The funds you have available for investment
depends on what you have authorized in regard to dividend reinvestment, plus
any cash investments made.  In every case, your available funds will be fully
invested in both whole and fractional shares of Common Stock (computed to four
decimal places).

17.    WHAT IS THE PRICE OF SHARES PURCHASED FOR THE PLAN?

       If shares for the Plan are being purchased on the open market or in
privately negotiated transactions, the price of such shares will be the
weighted average price at which the Independent Agent acquired the shares
allocated to Participants' accounts on the applicable Investment Date plus
applicable brokerage commissions and other fees.  If the Company is issuing new
shares of Common Stock, the price of such shares will be the average of the
high and low sales prices of the Company's Common Stock on the applicable
Investment Date reported as New York Stock Exchange Composite Transactions as
published in the Midwest Edition of The Wall Street Journal or other similar
financial publication.

18.    WHO PURCHASES THE SHARES FOR THE PLAN?

       The Company, at its discretion, may elect to satisfy the requirements of
the Plan with either unissued shares of Common Stock or shares of Common Stock
purchased on the open market. (See Question 10)  If the Company elects to
purchase shares of Common Stock on the open market, the Independent Agent will
make all such purchases necessary to meet the requirements of the Plan.  Other
than establishing the length of the investment period incorporated into the
Plan, the Company does not exercise any direct or indirect control over the
timing or price of purchases made by the Independent Agent on the open market.
If open market purchases are not made, the shares issued under the Plan will be
issued directly from the authorized and unissued shares of Common Stock of the
Company.

19.    ARE ANY FEES OR EXPENSES INCURRED BY PARTICIPANTS?

       Costs of administering the Plan will be paid by the Company, but
Participants will be required to pay brokerage commissions and other fees for
shares purchased in the open market and shares sold through the Plan.
Brokerage commissions will be at a negotiated rate established under the terms
of the Company's agreements with Independent Agents. (See Question 5)





                                       8


<PAGE>   10

SALES AND TERMINATION FROM THE PLAN

20.    MAY PARTICIPANTS SELL OR WITHDRAW ALL OR A PORTION OF THEIR SHARES FROM
       THE PLAN?

       Yes.  Any Participant may withdraw from the Plan, request that a
certificate be issued for Plan shares or request that Plan shares be sold and
the cash proceeds forwarded to the Participant.  Participation in the Plan is
entirely voluntary.  Participants may sell or withdraw all or a portion of
their shares by filling out the correspondence portion of their account
statement or by contacting Investor Services.

       A stock certificate for any whole number of shares will be issued from
your Plan account as soon as practicable after requested.  If you would like
stock certificates issued in a registration other than the name on your
account, contact Investor Services.

       Investor Services will aggregate Plan sale requests and place a market
order with the Independent Agent to sell such shares at least four times a
month.  The Participant will receive the proceeds of the sale less any
brokerage commission and any other fees as soon as practicable after the
settlement date for the applicable sale.

       If a Participant's request for a sale or withdrawal is received by
Investor Services on or soon after a dividend payment date, such request will
be processed as soon as practicable after reinvested dividends have been
allocated.

       If a Participant sells or withdraws all of the full shares in the
Participant's Plan account, Investor Services will automatically sell any
fractional share remaining in the account and forward the proceeds of the sale
to the Participant.


REPORTS TO PARTICIPANTS

21.    HOW WILL PARTICIPANTS BE ADVISED OF THEIR PURCHASE OF SHARES OF COMMON
       STOCK AND OTHER ACTIVITY IN THEIR PLAN ACCOUNTS?

       Participants will receive a quarterly statement as soon as practicable
following the end of each calendar quarter.  The last quarterly statement of
each calendar year will reflect year-to-date Plan activity.  In addition, a
statement will be provided in any month an account has Plan activity.  THESE
STATEMENTS ARE PARTICIPANTS' CONTINUING RECORD OF THE COST OF THEIR SHARES AND
SHOULD BE RETAINED FOR TAX PURPOSES.

       Participants will receive copies of the same communications sent to
other registered shareholders of Common Stock, including the Company's annual
report, notice of annual meeting and proxy statement, and certain tax
information.


CERTIFICATES

22.    WILL STOCK CERTIFICATES AUTOMATICALLY BE ISSUED FOR SHARES OF COMMON
       STOCK ACQUIRED UNDER THE PLAN?

       No.  The number of shares credited to your Plan account will be held by
Ameren Services, as agent, and will be shown on your statement of account.
This service protects against loss, theft or destruction of stock certificates.

       A certificate for any number of whole shares up to the full number of
shares credited to your Plan account will be issued to you if you so request in
writing. (See Question 20) Such request should be mailed to Investor Services.





                                       9



<PAGE>   11

       Shares credited to your Plan account may not be used as collateral.  If
you wish to use your Plan shares as collateral, you must request that a
certificate be issued in your name.  A certificate for fractional shares will
not be issued under any circumstances.


TRANSFER OF SHARES HELD IN THE PLAN

23.    CAN PLAN SHARES BE TRANSFERRED?

       Upon written request, Plan shares can be transferred into names other
than the account name, subject to compliance with any applicable laws and the
payment by the Participant of any applicable taxes, provided that the request
is accompanied by a duly executed Stock Power that bears the signature(s) of
the Participant(s) and the signature(s) is/are Medallion Guaranteed by a
commercial bank or member firm of the New York Stock Exchange that is a member
of either the STAMP, SEMP or MSP Medallion Guarantee programs.  Unless
instructed otherwise, Ameren Services will hold the transferred shares in an
account in the transferee's name in the Plan and apply the same dividend
reinvestment options as existed with respect to the transferred account.


SAFEKEEPING SERVICE FOR COMMON STOCK CERTIFICATES

24.    WHAT IS THE PLAN'S SAFEKEEPING SERVICE AND HOW DOES IT WORK?

       The Plan's safekeeping service allows you to deposit your Common Stock
certificate(s) into your Plan account.  The benefits of this service include
the convenience of keeping all of your shares in one place, and the protection
against the cost of replacing your certificates should they be lost, stolen or
destroyed.  If you would like to take advantage of this service, please contact
Investor Services.


INCOME TAXES

25.    WHAT ARE THE FEDERAL INCOME TAX CONSEQUENCES OF PARTICIPATION IN THE
       PLAN?

       In general, Participants in the Plan have the same federal income tax
obligations with respect to their dividends as do shareholders who are not Plan
Participants.  This means that dividends reinvested under the Plan are taxable
as having been received even though the Participants did not actually receive
them in cash but, instead, used them to purchase additional shares under the
Plan.

       The sale of shares by a Participant under the Plan may give rise to a
capital gain or loss, provided such shares are held as a capital asset by the
Participant.  Any such gain or loss will be measured by the difference between
the proceeds received by the Participant (net of commissions and fees) and the
Participant's tax basis in the shares sold.

       For Participants who are subject to U.S. withholding tax, backup
withholding or foreign taxes, the Company will withhold the required taxes from
the gross dividends or proceeds from the sale of shares.  The dividends or
proceeds received by the Participant, or dividends reinvested on behalf of the
Participant, will be net of the required taxes.

       The foregoing is only a general statement of federal income tax
consequences.  Each Participant should consult his or her own tax advisor as to
the specific application of the tax laws and regulations governing the Plan as
they relate to such Participant.  THE STATEMENTS OF ACCOUNT SENT TO
PARTICIPANTS SHOULD BE RETAINED FOR TAX PURPOSES.





                                       10



<PAGE>   12

                                 LEGAL OPINION

       Certain legal matters in connection with the Common Stock offered hereby
have been passed upon for the Company by William E. Jaudes, Esq., Vice
President and General Counsel of the Company.


                                    EXPERTS


       The financial statements incorporated in this Prospectus by reference to
the Annual Report to Shareholders which is incorporated by reference in Union
Electric's Form 10-K for the year ended December 31, 1996; the financial
statements incorporated into the Form S-4 of Union Electric dated November 13,
1995 by reference to the Annual Report to Shareholders which is incorporated by
reference in Union Electric's Form 10-K for the year ended December 31, 1995;
and the supplemental consolidated financial statements of Ameren as of December
31, 1996 and 1995 and for each of the three years in the period ended December
31, 1996 (except as such Ameren financial statements relate to CIPS and CIPSCO
Investment Company, which were audited by other independent accountants),
included on page 9 of Exhibit 99-2 to Ameren's Form 8-K dated December 31, 1997
incorporated in this Prospectus by reference to such Form 8-K, have each been
so incorporated in reliance on the reports of Price Waterhouse LLP, independent
accountants, given on the authority of said firm as experts in auditing and
accounting.

       The consolidated financial statements of CIPSCO Incorporated, as of
December 31, 1996 and 1995 and for each of the three years in the period ended
December 31, 1996 included in CIPSCO's 1996 Annual Report on Form 10-K
incorporated by reference in this Prospectus, and the consolidated financial
statements of CIPSCO Incorporated, as of December 31, 1995 and 1994 and for
each of the three years in the period ended December 31, 1995 included in
CIPSCO's 1995 Annual Report on Form 10-K incorporated by reference in this
Prospectus, have been audited by Arthur Andersen LLP, independent public
accountants, as indicated in their reports with respect thereto, and are
included herein in reliance upon the authority of said firm as experts in
giving said reports.





                                       11



<PAGE>   13





<TABLE>
===================================================         ===========================================================
 <S><C>
        This Prospectus  omits certain  information
 contained in  the registration statement which the
 Company  has   filed  with   the  Securities   and
 Exchange Commission  under the  Securities Act  of
 1933 and  to which  reference is  hereby made  for
 further information  with respect  to the  Company
 and the securities offered hereby.

                      CONTENTS

                                               PAGE                        AMEREN CORPORATION
                                               ----                                          

 Available Information . . . . . . . . . . . . .  2

 Incorporation of Certain Documents                                              DRPLUS

 by Reference  . . . . . . . . . . . . . . . . .  2                       DIVIDEND REINVESTMENT
                                                                         AND STOCK PURCHASE PLAN
 The Company . . . . . . . . . . . . . . . . . .  3

 Use of Proceeds . . . . . . . . . . . . . . . .  3
                                                                                                      
                                                                     ---------------------------------
 Description of the Plan . . . . . . . . . . . .  3

 Legal Opinion . . . . . . . . . . . . . . . .   11                            PROSPECTUS

 Experts . . . . . . . . . . . . . . . . . . .   11
                                                                                                      
                                                                     ---------------------------------

                                            
           ---------------------------------


        No  dealer,  salesman  or other  person has
 been  authorized  to  give any  information  or to
 make  any  representation  not  contained  in  the               Except  as   otherwise  indicated   by  the
 Prospectus  in connection  with the  offer made by         context, this  Prospectus speaks as  of the  date
 this  Prospectus  and,  if  given  or  made,  such         hereof  and  does  not  purport  to  reflect  any
 information or  representation must not be  relied         changes which may have occurred in the affairs of
 upon  as  having been  authorized by  the Company.         the Company thereafter.   Neither the delivery of
 This Prospectus  does not  constitute an  offering         this  Prospectus  nor  any  sale  made  hereunder
 by any  person in any State in which such offering         shall,   under  any   circumstances,  create   an
 may not lawfully be made.                                  implication  that there has been no change in the
                                                            affairs of the Company since the date hereof.
===================================================         ===========================================================
                                                                                                         
</TABLE>


<PAGE>   14



                PART II.  INFORMATION NOT REQUIRED IN PROSPECTUS

ITEM 14.    OTHER EXPENSES OF ISSUANCE AND DISTRIBUTION.

<TABLE>
                  <S>                                                                     <C>
                  Registration fee   . . . . . . . . . . . . . . . . . . . . . . . . .    $  53,813

                  Printing and engraving   . . . . . . . . . . . . . . . . . . . . . .       15,000*
                  Accounting Fees  . . . . . . . . . . . . . . . . . . . . . . . . . .       10,000*

                  Legal Fees . . . . . . . . . . . . . . . . . . . . . . . . . . . . .        5,000*

                  Miscellaneous expenses . . . . . . . . . . . . . . . . . . . . . . .        5,000*
                           Total . . . . . . . . . . . . . . . . . . . . . . . . . . .     $ 88,813*
                                                                                           ======== 

                 -----------------
                 * Estimated.

</TABLE>

ITEM 15.    INDEMNIFICATION OF DIRECTORS AND OFFICERS.

    Article IV of the Registrant's By-Laws, consistent with the applicable
provisions of the Missouri General and Business Corporation Law (the "MGBCL"),
provides for indemnification of directors and officers.  These provisions
provide that any person shall be indemnified for expenses and liabilities
imposed upon such person in connection with any threatened, pending or
completed action, suit, or proceeding, whether civil, criminal, administrative
or investigative, other than an action by or in the right of the Registrant, by
reason of the fact that such person is or was a director, officer, employee or
agent of the Registrant, or is or was serving at the request of the Registrant
as a director, officer, employee or agent of another corporation, partnership,
joint venture, trust or other enterprise, against expenses, including
attorneys' fees, judgments, fines and amounts paid in settlement actually and
reasonably incurred by such person in connection with such action, suit or
proceeding if such person acted in good faith and in a manner such person
reasonably believed to be in or not opposed to the best interests of the
Registrant, and, with respect to any criminal action or proceeding, had no
reasonable cause to believe his conduct was unlawful.

    In a proceeding brought by or in the right of the Registrant, no
indemnification shall be made with respect to any claim as to which an officer
or director has been adjudged to have been liable to the Registrant, unless the
court determines that such a person is reasonably and fairly entitled to
indemnification for expenses.  However, no indemnification shall be made in
respect of any claim, issue or matter as to which such person shall have been
adjudged to be liable for negligence or misconduct in the performance of his
duty to the Registrant unless and only to the extent that the court in which
the action or suit was brought determines upon application that, despite the
adjudication of liability and in view of all the circumstances of the case, the
person is fairly and reasonably entitled to indemnity for such expenses which
the court shall deem proper.

    The By-Laws, consistent with the applicable provisions of the MGBCL,
provide that indemnification shall be made by the Registrant only if a
determination has been made by a majority vote of a quorum of the disinterested
directors or by the shareholders or by independent legal counsel, that the
director or officer met the required standard of conduct.  The Registrant is
authorized to purchase liability insurance on behalf of an officer or director
whether or not the Registrant would otherwise have the power to indemnify such
a person.

    The By-Laws, consistent with the applicable provisions of the MGBCL,
further provide that, in addition to the indemnities described in the preceding
paragraphs, the Registrant will further indemnify its officers and directors to
the maximum extent permitted by law, provided that no indemnity may be given
for conduct that is adjudged to be knowingly fraudulent, deliberately
dishonest, or willful misconduct.





                                      II-1


<PAGE>   15





ITEM 16.  EXHIBITS.

    Exhibit No.
    ---------- 

          4.1        Article III of the Restated Certificate of Incorporation 
                     of the Registrant (incorporated by reference to Exhibit 
                     3(i) of the Form S-4 Registration Statement of the 
                     Registrant, Reg. No. 33-64165).

          4.2        By-Laws of the Registrant (incorporated by reference to 
                     Annex G of the Joint Proxy Statement/Prospectus included 
                     in the Form S-4 Registration Statement of the Registrant,
                     Reg. No. 33-64165).

          5          Opinion of William E. Jaudes as to the legality of the 
                     securities being issued.

         12          Computations of ratios of earnings to fixed charges 
                     (incorporated by reference to Exhibit 12 of each of the 
                     Forms 10-K, Forms 10-Q and Forms 8-K incorporated herein 
                     by reference).

         23.1        Consent of Price Waterhouse LLP.

         23.2        Consent of Arthur Andersen LLP.

         23.3        Consent of William E. Jaudes (included in Exhibit 5).

         24          Powers of Attorney.


ITEM 17.    UNDERTAKINGS.

    (a)     The undersigned Registrant hereby undertakes:

            (1)  To file, during any period in which offers or sales are being
                 made, a post-effective amendment to this registration
                 statement:

                 (i)      To include any prospectus required by Section
10(a)(3) of the Securities Act of 1933.

                 (ii)     To reflect in the prospectus any facts or events
                          arising after the effective date of the registration
                          statement (or the most recent post-effective
                          amendment thereof) which, individually or in the
                          aggregate, represent a fundamental change in the
                          information set forth in the registration statement.
                          Notwithstanding the foregoing, any increase or
                          decrease in volume of securities offered (if the
                          total dollar value of securities offered would not
                          exceed that which was registered) and any deviation
                          from the low or high end of the estimated maximum
                          offering range may be reflected in the form of
                          prospectus filed with the Commission pursuant to Rule
                          424(b) if, in the aggregate, the changes in volume
                          and price represent no more than a 20% change in the
                          maximum aggregate offering price set forth in the
                          "Calculation of Registration Fee" table in the
                          effective registration statement.

                 (iii)    To include any material information with respect to
                          the plan of distribution not previously disclosed in
                          the registration statement or any material change to
                          such information in the registration statement.





                                      II-2


<PAGE>   16




            (2)  That, for the purpose of determining any liability under the
Securities Act of 1933, each such post-effective amendment shall be deemed to
be a new registration statement relating to the securities offered therein, and
the offering of such securities at that time shall be deemed to be the initial
bona fide offering thereof.

Provided, however, that paragraphs (a)(l)(i) and (a)(l)(ii) do not apply if the
registration statement is on Form S-3, Form S-8 or Form F-3, and the
information required to be included in a post-effective amendment by those
paragraphs is contained in periodic reports filed with or furnished to the
Commission by the registrant pursuant to Section 13 or Section 15(d) of the
Securities Exchange Act of 1934 that are incorporated by reference in this
registration statement.

            (3)  To remove from registration by means of a post-effective
amendment any of the securities being registered which remain unsold at the
termination of the offering.

    (b)     The undersigned Registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act of 1933, each filing of the
Registrant's annual report pursuant to Section 13(a) or Section 15(d) of the
Securities Exchange Act of 1934 (and, where applicable, each filing of an
employee benefit plan's annual report pursuant to Section 15(d) of the
Securities Exchange Act of 1934) that is incorporated by reference in the
registration statement shall be deemed to be a new registration statement
relating to the securities offered therein, and the offering of such securities
at that time shall be deemed to be the initial bona fide offering thereof.

    (c)     Insofar as indemnification for liabilities arising under the
Securities Act of 1933 may be permitted to directors, officers and controlling
persons of the Registrant pursuant to the provisions referred to in Item 15 of
this registration statement, or otherwise, the Registrant has been advised that
in the opinion of the Securities and Exchange Commission such indemnification
is against public policy as expressed in the Act and is, therefore,
unenforceable.  In the event that a claim for indemnification against such
liabilities (other than the payment by the Registrant of expenses incurred or
paid by a director, officer or controlling person of the Registrant in the
successful defense of any action, suit or proceeding) is asserted by such
director, officer or controlling person in connection with the securities being
registered, the Registrant will, unless in the opinion of its counsel the
matter has been settled by controlling precedent, submit to a court of
appropriate jurisdiction the question of whether such indemnification by it is
against public policy as expressed in the Act and will be governed by the final
adjudication of such issue.





                                      II-3


<PAGE>   17



                                   SIGNATURES


    Pursuant to the requirements of the Securities Act of 1933, the Registrant
certifies that it has reasonable grounds to believe that it meets all
requirements for filing on Form S-3 and has duly caused this Registration
Statement on Form S-3 of the Registrant to be signed on its behalf by the
undersigned, thereunto duly authorized, in the City of St. Louis, and State of
Missouri, on January 2, 1998.

                                           AMEREN CORPORATION



                                           By  /s/Donald E. Brandt 
                                             ----------------------------------
                                               DONALD E. BRANDT
                                               Senior Vice President, Finance


    Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed by the following persons in the
capacities and on the date above indicated.


<TABLE>
<Capiton>
                         SIGNATURE                                                     TITLE
                         ---------                                                     -----
    <S>                                                                  <C>                                             


                                                                          Chairman, President and Chief
    /s/             Charles W. Mueller*                                   Executive Officer and Director
    ---------------------------------------------------                    (Principal Executive Officer)
                     CHARLES W. MUELLER                                                                 


    /s/               Donald E. Brandt                                    Senior Vice President, Finance
    ---------------------------------------------------            (Principal Financial and Accounting Officer)
                      DONALD E. BRANDT                                                                         


    /s/            Clifford L. Greenwalt*                                            Director
    ---------------------------------------------------                                      
                   CLIFFORD L. GREENWALT


    /s/            William E. Cornelius*                                             Director
    ---------------------------------------------------                                      
                   WILLIAM E. CORNELIUS


    /s/               Thomas A. Hays*                                                Director
    ---------------------------------------------------                                      
                       THOMAS A. HAYS


    /s/              Richard A. Liddy*                                               Director
    ---------------------------------------------------                                      
                      RICHARD A. LIDDY


    /s/                                                                              Director
    ---------------------------------------------------                                      
                      GORDAN R. LOHMAN


</TABLE>



                                      II-4


<PAGE>   18




<TABLE>
                 <S>                                                                            <C>  
                 /s/             Richard A. Lumpkin*                                              Director
                 ---------------------------------------------------
                                  RICHARD A. LUMPKIN

                                               

                 /s/            John Peters MacCarthy*                                            Director
                 ---------------------------------------------------                                      
                                JOHN PETERS MACCARTHY


                 /s/                                                                              Director
                 ---------------------------------------------------                                      
                                  HANNE M. MERRIMAN


                 /s/            Paul L. Miller, Jr.*                                              Director
                 ---------------------------------------------------                                      
                                 PAUL L. MILLER, JR.


                 /s/              Robert H. Quenon*                                               Director
                 ---------------------------------------------------                                      
                                   ROBERT H. QUENON


                 /s/              Harvey Saligman*                                                Director
                 ---------------------------------------------------                                      
                                   HARVEY SALIGMAN


                 /s/             Charles J. Schukai*                                              Director
                 ---------------------------------------------------                                      
                                  CHARLES J. SCHUKAI


                 /s/            Janet McAfee Weakley*                                             Director
                 ---------------------------------------------------                                      
                                JANET MCAFEE WEAKLEY


                 /s/                                                                              Director
                 ---------------------------------------------------                                      
                                  JAMES W. WOGSLAND


                                                   *By                /s/James C. Thompson            
                                                       -----------------------------------------------
                                                                        JAMES C. THOMPSON
                                                                          Attorney-In-Fact
</TABLE>





                                      II-5


<PAGE>   19




                                 EXHIBIT INDEX


      EXHIBIT NO.
      ---------- 

          4.1        Article III of the Restated Certificate of Incorporation 
                     of the Registrant (incorporated by reference to Exhibit 
                     3(i) of the Form S-4 Registration Statement of the 
                     Registrant, Reg. No. 33-64165).

          4.2        By-Laws of the Registrant (incorporated by reference to 
                     Annex G of the Joint Proxy Statement/Prospectus included 
                     in the Form S-4 Registration Statement of the Registrant,
                     Reg. No. 33-64165).

          5          Opinion of William E. Jaudes as to the legality of the 
                     securities being issued.

         12          Computations of ratios of earnings to fixed charges 
                     (incorporated by reference to Exhibit 12 of each of the 
                     Forms 10-K, Forms 10-Q and Forms 8-K incorporated herein 
                     by reference).

         23.1        Consent of Price Waterhouse LLP.

         23.2        Consent of Arthur Andersen LLP.

         23.3        Consent of William E. Jaudes (included in Exhibit 5).

         24          Powers of Attorney.





                                      II-6



<PAGE>   1



                                                                       EXHIBIT 5


                                January 5, 1998


Ameren Corporation
1901 Chouteau Avenue
St. Louis, Missouri  63103

  Re:      Registration Statement on Form S-3 Relating to 4,200,000 Shares of
Common Stock

Ladies and Gentlemen:

        I have examined the Registration Statement on Form S-3 (the
"Registration Statement") filed by Ameren Corporation, a Missouri corporation
(the "Company"), with the Securities and Exchange Commission on January 5, 1998
in connection with the registration under the Securities Act of 1933, as
amended, of 4,200,000 shares of the Common Stock, $0.01 par value per share
(the "Common Stock"), of the Company to be offered and sold pursuant to its
DRPlus Dividend Reinvestment and Stock Purchase Plan.

        As Vice President and General Counsel of the Company, I have examined
the Restated Certificate of Incorporation and the By-laws of the Company, each
as amended to the date hereof, the records of corporate proceedings and other
actions taken by the Company in connection with the authorization, issuance and
sale of the Common Stock and such other documents and materials as I have
deemed necessary or appropriate to enable me to deliver this opinion.

        Based upon the foregoing, I am of the opinion that:

        Subject to (i) compliance with applicable state securities laws and
(ii) the filing and effectiveness of the Registration Statement with the
Securities and Exchange Commission, the Common Stock, when issued and sold in
the manner described in the Registration Statement, will be legally issued,
fully paid and nonassessable.

        I hereby consent to the filing of this opinion as an exhibit to the
Registration Statement to the use of my name under the caption "Legal Opinion"
in the Prospectus forming a part of the Registration Statement.

                                           Yours truly,



                                           /s/William E. Jaudes 
                                           -------------------------
                                           William E. Jaudes
                                           Vice President and General Counsel
                                           Ameren Corporation








<PAGE>   1



                                                                    EXHIBIT 23.1


                       CONSENT OF INDEPENDENT ACCOUNTANTS


         We hereby consent to the incorporation by reference in the Prospectus
constituting part of this Registration Statement on Form S-3 of our report
dated February 4, 1997, which appears on page 16 of Union Electric Company's
1996 Annual Report to Shareholders which is incorporated by reference in Union
Electric Company's Annual Report on Form 10-K for the year ended December 31,
1996.  We also consent to the incorporation by reference in the Prospectus
constituting part of this Registration Statement on Form S-3 of our report
dated December 17, 1997, which appears on page 9 of Exhibit 99-2 to the Ameren
Corporation Current Report on Form 8-K dated December 31, 1997, with respect to
the supplemental consolidated financial statements of Ameren Corporation as of
December 31, 1996 and 1995 and for each of the three years in the period ended
December 31, 1996, except as such Ameren Corporation financial statements
relate to Central Illinois Public Service Company and CIPSCO Investment
Company.  The Central Illinois Public Service Company and CIPSCO Investment
Company financial statements were audited by another independent accountant.
We also consent to the incorporation by reference in the Registration Statement
on Form S-4 (No. 33-64165) of Ameren Corporation dated November 13, 1995 (the
"Form S-4") of our report dated February 1, 1996, which appears on page 16 of
Union Electric Company's 1995 Annual Report to Shareholders which is
incorporated by reference in Union Electric Company's Annual Report on Form
10-K for the year ended December 31, 1995, which Form 10-K is incorporated by
reference in the Form S-4.  The Form S-4 is incorporated by reference into the
Prospectus constituting part of this Registration Statement on Form S-3.  We
also consent to the application of our reports to the Financial Statement
Schedules, which appear on pages 13 (1996 Form 10-K) and 12 (1995 Form 10-K) of
Union Electric Company's Annual Reports on Form 10-K, for each of the four
years in the period ended December 31, 1996, when such Schedules are read in
conjunction with the financial statements referred to in our reports dated
February 4, 1997 and February 1, 1996.  We also consent to the reference to us
under the heading "Experts" in such Prospectus.



/s/Price Waterhouse LLP  
- -----------------------
Price Waterhouse LLP
St. Louis, Missouri
December 31, 1997







<PAGE>   1



                                                                    EXHIBIT 23.2


                              ARTHUR ANDERSEN LLP




                   CONSENT OF INDEPENDENT PUBLIC ACCOUNTANTS


         As independent public accountants, we hereby consent to the
incorporation by reference in this Registration Statement of our reports dated
January 31, 1997 and January 26, 1996 included in CIPSCO Incorporated's Form
10-K for the years ended December 31, 1996 and 1995, respectively, and to all
references to our Firm included in this Registration Statement.



                                                /s/ARTHUR ANDERSEN LLP          
                                                -------------------------------
                                                ARTHUR ANDERSEN LLP

Chicago, Illinois
December 30, 1997







<PAGE>   1



                                                                      EXHIBIT 24



                               POWER OF ATTORNEY


         KNOW ALL MEN BY THESE PRESENTS:  That the undersigned Charles W.
Mueller hereby appoints Donald E. Brandt and/or James C. Thompson the true and
lawful attorneys-in-fact of the undersigned, for and in the name, place and
stead of the undersigned, to affix the name of the undersigned as a Director
and as Chairman of The Board, President, and Chief Executive Officer, of Ameren
Corporation to a Registration Statement(s) and any amendments thereto to be
filed with the Securities and Exchange Commission under the Securities Act of
1933, covering the issue of Common Stock under the dividend reinvestment and
stock purchase plan, stock incentive plan, and savings investment plans, as
authorized by the Company's Board of Directors on December 17, 1997, and, for
the performance of the same acts, each with power to appoint in their place and
stead and as their substitute, one or more attorneys-in-fact for the
undersigned, with full power of revocation; hereby ratifying and confirming all
that said attorneys-in-fact may do by virtue hereof.

         IN WITNESS WHEREOF, the undersigned has hereunto set his hand and seal
this 23rd day of December, 1997.



                                        Charles W. Mueller              (L.S.)
                                        --------------------------------

STATE OF MISSOURI            )
                             )  SS.
CITY OF ST. LOUIS            )


         On this 23rd day of December, 1997, before me the undersigned Notary
Public in and for said State, personally appeared Charles W.  Mueller, known to
me to be the person described in and who executed the foregoing power of
attorney and acknowledged to me that he executed the same as his free act and
deed for the purposes therein stated.

         IN TESTIMONY WHEREOF, I have hereunto set my hand and affixed my
official seal.



                                        Barbara Lungwitz                   
                                        --------------------------------


<PAGE>   2




                                                                      EXHIBIT 24



                               POWER OF ATTORNEY


         KNOW ALL MEN BY THESE PRESENTS:  That the undersigned Donald E. Brandt
hereby appoints Charles W. Mueller and/or Donald E. Brandt and/or James C.
Thompson the true and lawful attorneys-in-fact of the undersigned, for and in
the name, place and stead of the undersigned, to affix the name of the
undersigned as a Director of Ameren Corporation to a Registration Statement(s)
and any amendments thereto to be filed with the Securities and Exchange
Commission under the Securities Act of 1933, covering the issue of Common Stock
under the dividend reinvestment and stock purchase plan, stock incentive plan,
and savings investment plans, as authorized by the Company's Board of Directors
on December 17, 1997, and, for the performance of the same acts, each with
power to appoint in their place and stead and as their substitute, one or more
attorneys-in-fact for the undersigned, with full power of revocation; hereby
ratifying and confirming all that said attorneys-in-fact may do by virtue
hereof.
         IN WITNESS WHEREOF, the undersigned has hereunto set his hand and seal
this 23rd day of December, 1997.


                                         Donald E. Brandt           (L.S.)
                                         ---------------------------


STATE OF MISSOURI            )
                             )  SS.
CITY OF ST.LOUIS             )


         On this 23rd day of December, 1997, before me the undersigned Notary
Public in and for said State, personally appeared December, known to me to be
the person described in and who executed the foregoing power of attorney and
acknowledged to me that he executed the same as his free act and deed for the
purposes therein stated.

         IN TESTIMONY WHEREOF, I have hereunto set my hand and affixed my
official seal.



                                         Barbara Lungwitz                  
                                         ---------------------------


<PAGE>   3



                                                                      EXHIBIT 24



                               POWER OF ATTORNEY


         KNOW ALL MEN BY THESE PRESENTS:  That the undersigned Clifford L.
Greenwalt hereby appoints Charles W. Mueller and/or Donald E. Brandt and/or
James C. Thompson the true and lawful attorneys-in-fact of the undersigned, for
and in the name, place and stead of the undersigned, to affix the name of the
undersigned as a Director of Ameren Corporation to a Registration Statement(s)
and any amendments thereto to be filed with the Securities and Exchange
Commission under the Securities Act of 1933, covering the issue of Common Stock
under the dividend reinvestment and stock purchase plan, stock incentive plan,
and savings investment plans, as authorized by the Company's Board of Directors
on December 17, 1997, and, for the performance of the same acts, each with
power to appoint in their place and stead and as their substitute, one or more
attorneys-in-fact for the undersigned, with full power of revocation; hereby
ratifying and confirming all that said attorneys-in-fact may do by virtue
hereof.

         IN WITNESS WHEREOF, the undersigned has hereunto set his hand and seal
this 31st day of December, 1997.


                                        Clifford L. Greenwalt        (L.S.)
                                        -----------------------------


STATE OF MISSOURI            )
                             )  SS.
CITY OF ST. LOUIS            )


         On this 31st day of December, 1997, before me the undersigned Notary
Public in and for said State, personally appeared December, known to me to be
the person described in and who executed the foregoing power of attorney and
acknowledged to me that he executed the same as his free act and deed for the
purposes therein stated.

         IN TESTIMONY WHEREOF, I have hereunto set my hand and affixed my
official seal.



                                        Barbara Lungwitz                  
                                        -----------------------------



<PAGE>   4




                                                                      EXHIBIT 24



                               POWER OF ATTORNEY


         KNOW ALL MEN BY THESE PRESENTS:  That the undersigned William E.
Cornelius hereby appoints Charles W. Mueller and/or Donald E. Brandt and/or
James C. Thompson the true and lawful attorneys-in-fact of the undersigned, for
and in the name, place and stead of the undersigned, to affix the name of the
undersigned as a Director of Ameren Corporation to a Registration Statement(s)
and any amendments thereto to be filed with the Securities and Exchange
Commission under the Securities Act of 1933, covering the issue of Common Stock
under the dividend reinvestment and stock purchase plan, stock incentive plan,
and savings investment plans, as authorized by the Company's Board of Directors
on December 17, 1997, and, for the performance of the same acts, each with
power to appoint in their place and stead and as their substitute, one or more
attorneys-in-fact for the undersigned, with full power of revocation; hereby
ratifying and confirming all that said attorneys-in-fact may do by virtue
hereof.
         IN WITNESS WHEREOF, the undersigned has hereunto set his hand and seal
this 19th day of December, 1997.


                                        William E. Cornelius         (L.S.)
                                        -----------------------------


STATE OF MISSOURI            )
                             )  SS.
CITY OF ST.LOUIS             )


         On this 19th day of December, 1997, before me the undersigned Notary
Public in and for said State, personally appeared December, known to me to be
the person described in and who executed the foregoing power of attorney and
acknowledged to me that he executed the same as his free act and deed for the
purposes therein stated.

         IN TESTIMONY WHEREOF, I have hereunto set my hand and affixed my
official seal.



                                        Barbara Lungwitz                  
                                        -----------------------------



<PAGE>   5




                                                                      EXHIBIT 24



                               POWER OF ATTORNEY


         KNOW ALL MEN BY THESE PRESENTS:  That the undersigned Thomas A. Hays
hereby appoints Charles W. Mueller and/or Donald E. Brandt and/or James C.
Thompson the true and lawful attorneys-in-fact of the undersigned, for and in
the name, place and stead of the undersigned, to affix the name of the
undersigned as a Director of Ameren Corporation to a Registration Statement(s)
and any amendments thereto to be filed with the Securities and Exchange
Commission under the Securities Act of 1933, covering the issue of Common Stock
under the dividend reinvestment and stock purchase plan, stock incentive plan,
and savings investment plans, as authorized by the Company's Board of Directors
on December 17, 1997, and, for the performance of the same acts, each with
power to appoint in their place and stead and as their substitute, one or more
attorneys-in-fact for the undersigned, with full power of revocation; hereby
ratifying and confirming all that said attorneys-in-fact may do by virtue
hereof.
         IN WITNESS WHEREOF, the undersigned has hereunto set his hand and seal
this 20th day of December, 1997.


                                         Thomas A. Hays            (L.S.)
                                         --------------------------


STATE OF MISSOURI            )
                             )  SS.
CITY OF ST.LOUIS             )


         On this 20th day of December, 1997, before me the undersigned Notary
Public in and for said State, personally appeared December, known to me to be
the person described in and who executed the foregoing power of attorney and
acknowledged to me that he executed the same as his free act and deed for the
purposes therein stated.

         IN TESTIMONY WHEREOF, I have hereunto set my hand and affixed my
official seal.



                                         Barbara Lungwitz                  
                                         --------------------------


<PAGE>   6




                                                                      EXHIBIT 24



                               POWER OF ATTORNEY


         KNOW ALL MEN BY THESE PRESENTS:  That the undersigned Richard A. Liddy
hereby appoints Charles W. Mueller and/or Donald E. Brandt and/or James C.
Thompson the true and lawful attorneys-in-fact of the undersigned, for and in
the name, place and stead of the undersigned, to affix the name of the
undersigned as a Director of Ameren Corporation to a Registration Statement(s)
and any amendments thereto to be filed with the Securities and Exchange
Commission under the Securities Act of 1933, covering the issue of Common Stock
under the dividend reinvestment and stock purchase plan, stock incentive plan,
and savings investment plans, as authorized by the Company's Board of Directors
on December 17, 1997, and, for the performance of the same acts, each with
power to appoint in their place and stead and as their substitute, one or more
attorneys-in-fact for the undersigned, with full power of revocation; hereby
ratifying and confirming all that said attorneys-in-fact may do by virtue
hereof.
         IN WITNESS WHEREOF, the undersigned has hereunto set his hand and seal
this 23rd day of December, 1997.


                                          Richard A. Liddy           (L.S.)
                                          ---------------------------


STATE OF MISSOURI            )
                             )  SS.
CITY OF ST.LOUIS             )


         On this 23rd day of December, 1997, before me the undersigned Notary
Public in and for said State, personally appeared December, known to me to be
the person described in and who executed the foregoing power of attorney and
acknowledged to me that he executed the same as his free act and deed for the
purposes therein stated.

         IN TESTIMONY WHEREOF, I have hereunto set my hand and affixed my
official seal.



                                           Barbara Lungwitz                  
                                          ---------------------------


<PAGE>   7




                                                                      EXHIBIT 24



                               POWER OF ATTORNEY


         KNOW ALL MEN BY THESE PRESENTS:  That the undersigned Richard A.
Lumpkin hereby appoints Charles W. Mueller and/or Donald E. Brandt and/or James
C. Thompson the true and lawful attorneys-in-fact of the undersigned, for and
in the name, place and stead of the undersigned, to affix the name of the
undersigned as a Director of Ameren Corporation to a Registration Statement(s)
and any amendments thereto to be filed with the Securities and Exchange
Commission under the Securities Act of 1933, covering the issue of Common Stock
under the dividend reinvestment and stock purchase plan, stock incentive plan,
and savings investment plans, as authorized by the Company's Board of Directors
on December 17, 1997, and, for the performance of the same acts, each with
power to appoint in their place and stead and as their substitute, one or more
attorneys-in-fact for the undersigned, with full power of revocation; hereby
ratifying and confirming all that said attorneys-in-fact may do by virtue
hereof.
         IN WITNESS WHEREOF, the undersigned has hereunto set his hand and seal
this 31st day of December, 1997.


                                          Richard A. Lumpkin          (L.S.)
                                          ----------------------------


STATE OF ILLINOIS            )
                             )  SS.
CITY OF MATTOON              )


         On this 31st day of December, 1997, before me the undersigned Notary
Public in and for said State, personally appeared December, known to me to be
the person described in and who executed the foregoing power of attorney and
acknowledged to me that he executed the same as his free act and deed for the
purposes therein stated.

         IN TESTIMONY WHEREOF, I have hereunto set my hand and affixed my
official seal.



                                          Renee Spitz                    
                                          ----------------------------


<PAGE>   8




                                                                      EXHIBIT 24



                               POWER OF ATTORNEY


         KNOW ALL MEN BY THESE PRESENTS:  That the undersigned John Peters
MacCarthy hereby appoints Charles W. Mueller and/or Donald E. Brandt and/or
James C. Thompson the true and lawful attorneys-in-fact of the undersigned, for
and in the name, place and stead of the undersigned, to affix the name of the
undersigned as a Director of Ameren Corporation to a Registration Statement(s)
and any amendments thereto to be filed with the Securities and Exchange
Commission under the Securities Act of 1933, covering the issue of Common Stock
under the dividend reinvestment and stock purchase plan, stock incentive plan,
and savings investment plans, as authorized by the Company's Board of Directors
on December 17, 1997, and, for the performance of the same acts, each with
power to appoint in their place and stead and as their substitute, one or more
attorneys-in-fact for the undersigned, with full power of revocation; hereby
ratifying and confirming all that said attorneys-in-fact may do by virtue
hereof.
         IN WITNESS WHEREOF, the undersigned has hereunto set his hand and seal
this 19th day of December, 1997.


                                       John Peters MacCarthy        (L.S.)
                                       -----------------------------


STATE OF MISSOURI            )
                             )  SS.
CITY OF ST.LOUIS             )


         On this 19th day of December, 1997, before me the undersigned Notary
Public in and for said State, personally appeared December, known to me to be
the person described in and who executed the foregoing power of attorney and
acknowledged to me that he executed the same as his free act and deed for the
purposes therein stated.

         IN TESTIMONY WHEREOF, I have hereunto set my hand and affixed my
official seal.



                                       Barbara Lungwitz                  
                                       -----------------------------



<PAGE>   9




                                                                      EXHIBIT 24



                               POWER OF ATTORNEY


         KNOW ALL MEN BY THESE PRESENTS:  That the undersigned Paul L. Miller
hereby appoints Charles W. Mueller and/or Donald E. Brandt and/or James C.
Thompson the true and lawful attorneys-in-fact of the undersigned, for and in
the name, place and stead of the undersigned, to affix the name of the
undersigned as a Director of Ameren Corporation to a Registration Statement(s)
and any amendments thereto to be filed with the Securities and Exchange
Commission under the Securities Act of 1933, covering the issue of Common Stock
under the dividend reinvestment and stock purchase plan, stock incentive plan,
and savings investment plans, as authorized by the Company's Board of Directors
on December 17, 1997, and, for the performance of the same acts, each with
power to appoint in their place and stead and as their substitute, one or more
attorneys-in-fact for the undersigned, with full power of revocation; hereby
ratifying and confirming all that said attorneys-in-fact may do by virtue
hereof.
         IN WITNESS WHEREOF, the undersigned has hereunto set his hand and seal
this 31st day of December, 1997.


                                         Paul L. Miller            (L.S.)
                                         --------------------------


STATE OF MISSOURI            )
                             )  SS.
CITY OF ST. LOUIS            )


         On this 31st day of December, 1997, before me the undersigned Notary
Public in and for said State, personally appeared December, known to me to be
the person described in and who executed the foregoing power of attorney and
acknowledged to me that he executed the same as his free act and deed for the
purposes therein stated.

         IN TESTIMONY WHEREOF, I have hereunto set my hand and affixed my
official seal.



                                         Barbara Lungwitz                  
                                         --------------------------


<PAGE>   10




                                                                      EXHIBIT 24



                               POWER OF ATTORNEY


         KNOW ALL MEN BY THESE PRESENTS:  That the undersigned Robert H. Quenon
hereby appoints Charles W. Mueller and/or Donald E. Brandt and/or James C.
Thompson the true and lawful attorneys-in-fact of the undersigned, for and in
the name, place and stead of the undersigned, to affix the name of the
undersigned as a Director of Ameren Corporation to a Registration Statement(s)
and any amendments thereto to be filed with the Securities and Exchange
Commission under the Securities Act of 1933, covering the issue of Common Stock
under the dividend reinvestment and stock purchase plan, stock incentive plan,
and savings investment plans, as authorized by the Company's Board of Directors
on December 17, 1997, and, for the performance of the same acts, each with
power to appoint in their place and stead and as their substitute, one or more
attorneys-in-fact for the undersigned, with full power of revocation; hereby
ratifying and confirming all that said attorneys-in-fact may do by virtue
hereof.
         IN WITNESS WHEREOF, the undersigned has hereunto set his hand and seal
this 24th day of December, 1997.


                                         Robert H. Quenon           (L.S.)
                                         ---------------------------


STATE OF MISSOURI            )
                             )  SS.
CITY OF ST. LOUIS            )


         On this 24th day of December, 1997, before me the undersigned Notary
Public in and for said State, personally appeared December, known to me to be
the person described in and who executed the foregoing power of attorney and
acknowledged to me that he executed the same as his free act and deed for the
purposes therein stated.

         IN TESTIMONY WHEREOF, I have hereunto set my hand and affixed my
official seal.



                                         Barbara Lungwitz                  
                                         ---------------------------




<PAGE>   11




                                                                      EXHIBIT 24



                               POWER OF ATTORNEY


         KNOW ALL MEN BY THESE PRESENTS:  That the undersigned Harvey Saligman
hereby appoints Charles W. Mueller and/or Donald E. Brandt and/or James C.
Thompson the true and lawful attorneys-in-fact of the undersigned, for and in
the name, place and stead of the undersigned, to affix the name of the
undersigned as a Director of Ameren Corporation to a Registration Statement(s)
and any amendments thereto to be filed with the Securities and Exchange
Commission under the Securities Act of 1933, covering the issue of Common Stock
under the dividend reinvestment and stock purchase plan, stock incentive plan,
and savings investment plans, as authorized by the Company's Board of Directors
on December 17, 1997, and, for the performance of the same acts, each with
power to appoint in their place and stead and as their substitute, one or more
attorneys-in-fact for the undersigned, with full power of revocation; hereby
ratifying and confirming all that said attorneys-in-fact may do by virtue
hereof.
         IN WITNESS WHEREOF, the undersigned has hereunto set his hand and seal
this 23rd day of December, 1997.


                                        Harvey Saligman           (L.S.)
                                        --------------------------


STATE OF MISSOURI            )
                             )  SS.
CITY OF ST.LOUIS             )


         On this 23rd day of December, 1997, before me the undersigned Notary
Public in and for said State, personally appeared December, known to me to be
the person described in and who executed the foregoing power of attorney and
acknowledged to me that he executed the same as his free act and deed for the
purposes therein stated.

         IN TESTIMONY WHEREOF, I have hereunto set my hand and affixed my
official seal.



                                        Barbara Lungwitz                  
                                        --------------------------



<PAGE>   12





                                                                      EXHIBIT 24



                               POWER OF ATTORNEY


         KNOW ALL MEN BY THESE PRESENTS:  That the undersigned Charles J.
Schukai hereby appoints Charles W. Mueller and/or Donald E. Brandt and/or James
C. Thompson the true and lawful attorneys-in-fact of the undersigned, for and
in the name, place and stead of the undersigned, to affix the name of the
undersigned as a Director of Ameren Corporation to a Registration Statement(s)
and any amendments thereto to be filed with the Securities and Exchange
Commission under the Securities Act of 1933, covering the issue of Common Stock
under the dividend reinvestment and stock purchase plan, stock incentive plan,
and savings investment plans, as authorized by the Company's Board of Directors
on December 17, 1997, and, for the performance of the same acts, each with
power to appoint in their place and stead and as their substitute, one or more
attorneys-in-fact for the undersigned, with full power of revocation; hereby
ratifying and confirming all that said attorneys-in-fact may do by virtue
hereof.
         IN WITNESS WHEREOF, the undersigned has hereunto set his hand and seal
this 23rd day of December, 1997.


                                      Charles J. Schukai          (L.S.)
                                      ----------------------------


STATE OF MISSOURI            )
                             )  SS.
CITY OF ST.LOUIS             )


         On this 23rd day of December, 1997, before me the undersigned Notary
Public in and for said State, personally appeared December, known to me to be
the person described in and who executed the foregoing power of attorney and
acknowledged to me that he executed the same as his free act and deed for the
purposes therein stated.

         IN TESTIMONY WHEREOF, I have hereunto set my hand and affixed my
official seal.



                                      Barbara Lungwitz                  
                                      ----------------------------



<PAGE>   13




                                                                      EXHIBIT 24



                               POWER OF ATTORNEY


         KNOW ALL MEN BY THESE PRESENTS:  That the undersigned Janet McAfee
Weakley hereby appoints Charles W. Mueller and/or Donald E. Brandt and/or James
C. Thompson the true and lawful attorneys-in-fact of the undersigned, for and
in the name, place and stead of the undersigned, to affix the name of the
undersigned as a Director of Ameren Corporation to a Registration Statement(s)
and any amendments thereto to be filed with the Securities and Exchange
Commission under the Securities Act of 1933, covering the issue of Common Stock
under the dividend reinvestment and stock purchase plan, stock incentive plan,
and savings investment plans, as authorized by the Company's Board of Directors
on December 17, 1997, and, for the performance of the same acts, each with
power to appoint in their place and stead and as their substitute, one or more
attorneys-in-fact for the undersigned, with full power of revocation; hereby
ratifying and confirming all that said attorneys-in-fact may do by virtue
hereof.
         IN WITNESS WHEREOF, the undersigned has hereunto set his hand and seal
this 19th day of December, 1997.


                                        Janet M. Weakley           (L.S.)
                                        ---------------------------


STATE OF MISSOURI            )
                             )  SS.
CITY OF ST.LOUIS             )


         On this 19th day of December, 1997, before me the undersigned Notary
Public in and for said State, personally appeared December, known to me to be
the person described in and who executed the foregoing power of attorney and
acknowledged to me that he executed the same as his free act and deed for the
purposes therein stated.

         IN TESTIMONY WHEREOF, I have hereunto set my hand and affixed my
official seal.



                                        Kathleen D. O'Reilly                
                                        ---------------------------








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